1 #!/usr/bin/perl -w
  2 use strict;
  3 my %dup;
  4 while(<>){
  5 my @row=split(/\s+/,$_);
  6 $dup{$row[3]}=$dup{$row[3]}+1; #if change to $dup{$row[3]}++, it will run smoothly no error report
  7 }
  8
  9 foreach my $id (keys %dup){
 10 if ($dup{$id}>1) {
 11 print "$id\t$dup{$id}\n";
 12 }
 13 }